This invention relates to the transfer of impressions from one surface to another by the use of coatings. More particularly, the invention relates to improved transfer images obtained employing a lower concentration of transfer materials than would normally be required in prior art coating processes for obtaining the same desired result.
Heretofore carbon papers have been made primarily by applying to a flexible foundation a single layer of a coating composition comprised of waxes or wax-like materials to which a colorant or blend of colorants had been added. Additional materials could be added to the coating mixture when special properties were desired. The ensuing mixture is then generally applied to a substrate such as paper either in molten form or in solution with one or more organic solvents. In the case of a paper substrate the resulting product is commonly known as carbon or transfer paper. The product is also known as "one-time" carbon paper when it is intended for a single use.
The usual manufacturing procedure is relatively slow, requires special equipment for the application of organic solvent coatings or molten coatings and may result in the application of relatively thick coatings to the substrates. Such coatings may be unsatisfactory where the transfer medium is to be used in producing a large number of copies and in any case may produce images of less sharp definition than where lighter and/or harder coatings are employed. Moreover, such waxy colored coatings have a tendency to smudge the hands and also the underlying copy papers. In addition, when the coating is relatively thick it represents a significant cost factor. The constituents of the coating have been the subject of demand pressure, which in view of supply shortages, has given rise to a continuously increasing element of overall cost.
Various attempts have been made to solve at least some of the above-identified problems as exemplified by U.S. Pat. No. 2,931,752 issued Apr. 5, 1960. According to this prior art teaching, a transfer layer is employed in which the color carrying material is primarily water-insoluble wax but which is of such a nature that it can be spread directly from a water dispersion rather than being applied in a molten condition with attendant temperature control problems. Although at the time, the teachings of this patent represented a significant advancement over the prior art, the coatings used in accordance with this patent are costly and are now in short supply. In addition, and most significantly, these same coatings demonstrate reduced image definition by comparison with standard coatings of comparable thickness.
Aqueous coatings have also been used in the production of donor-receptor copy papers to provide what is commonly known as "mated" systems. One example is U.S. Pat. No. 3,635,747. Not only are there the disadvantages and waste of the mated system, the transfer images again, tend to have reduced definition.
Similarly in Swiss Pat. No. 465,386 and German Pat. No. 1,421,444 the use of aqueous coatings is accompanied by production and technical disadvantages as well as a failure to obtain the desired image definition.
Ideally, a method of coating substrates whereby the problems of reduced transfer image definition and smudging are eliminated but which at the same time affords a product of potentially lower cost would be beneficial to both the industry and consumer at large.
Accordingly, it is the principal object of the immediate invention to provide a method of coating transfer media such that the resultant transfer image is well-defined and demonstrates an improved quality over the transfer image obtained from conventionally-coated transfer media.
Another object of the present invention is to reduce the amount of wax and/or wax-like materials needed in the manufacture of transfer coatings.
It is a further object of the present invention to prepare transfer media to the carbon paper type which are cleaner to the touch and which pressure-release images are more smudge-resistant than those heretofore known.
Yet another object of this invention is to produce a one-time carbon paper which is lighter in weight than conventional one-time carbon paper.
The above and additional objects of this invention, which will be more readily apparent on reviewing the ensuing disclosure, are accomplished in accordance with the following summary.